Early exhaust gas purifying systems included a cylindrically shaped catalyst coated honeycomb substrate having a flat inlet face. Although this conventional system effectively converted pollutants into non-toxic gases, the design tended to exhibit non-uniform flow distribution. Specifically, the high velocity exhaust gases which were emitted from a relatively small diameter exhaust pipe of an internal combustion engine did not dissipate when passing from the exhaust pipe into the larger diameter casing in which the catalyst substrate was located. As a result, a large portion of the high velocity exhaust gas tended to flow through the center of the honeycomb structure than through the peripheral portion. As a result of this non-uniform flow distribution of exhaust gases through the center, these catalytic converter systems exhibited a loss of conversion efficiency, as well as deactivation of the converter in the region of highest flow velocity. In addition, the non-uniform flow distribution tended to result in a higher pressure drop across the catalyst structure which in turn results in the decreased engine performance.
A variety of attempts have been made to increase the efficiency of the catalytic converter structure. These attempts have included altering the expansion angle between the inlet and the casing. However, the resulting flow still creates non-uniform flow distribution.
Therefore, a need exists for a catalyst substrate that can enhance uniform gas flow through the substrate and hence the catalytic converter. The need also exists for a catalyst substrate that can provide greater surface area without requiring increased casing volume. The further need exists for forming a catalyst substrate by an economically acceptable process, wherein the resulting substrate can be formed to match the profile of a desired casing or can. The need further exists for a method and apparatus for manufacturing substrates that can have a shaped inlet and outlet face.